We have never had any trouble from a Park Ranger or Law enforcement while in a park. It's pretty much common sense, and we don't read the rules. Treat the park like you would your own backyard. Consider it public property. Don't hang stuff on nature, don't park on nature.
The only issue we have had years back (already ranted long ago) was a border crossing into Canada. WOW! Anyway..... perhaps they were looking out for something.
As far as Park Rangers though, no problems.
There however is a rule we don't like. Some campgrounds have a maximum of 6 people. Having 5 children my wife and I go over that. We ask the person at the desk 'if that is okay'. We have not been told no yet. The explanation one lady gave was "too many people will trample the vegetation". Another person told us "oh this rule is to prevent many people from showing up to a site having a loud party".... Who knows. I think they see we are a family and wave us on through. But it is difficult to see more and more campground adapting that rule. But we do ask. If they ever say "no", we go to walmart or national forest for the night.